KAREN NELSON MOORE, Circuit Judge. In 2006, Oliver Higgins (“Higgins”) was indicted and charged with six counts: possession with intent to distribute cocaine base, possession with intent to distribute cocaine, possession with intent to distribute marijuana, possession of counterfeit currency with intent to defraud, felon in possession of a firearm, and possession of a firearm in connection with a drug-trafficking crime. Before trial, Higgins moved to suppress all of the evidence stemming from the search of his apartment on the grounds that the warrant lacked probable cause. The district court denied this motion. At trial, the jury convicted Higgins of five of the six counts (all of the counts except the third, marijuana-based crime). The district court sentenced Higgins to an effective sentence of life imprisonment plus five years.

On appeal, Higgins raises two arguments. First, Higgins asserts that the district court erred in denying his motion to suppress because the search warrant lacked probable cause. Second, Higgins presents three arguments for why the district court erred in imposing a sentence of life imprisonment: (1) although the jury convicted Higgins of an offense involving cocaine base, his sentence violated the Sixth Amendment because it was based on a judicial finding that the offense involved crack cocaine; (2) Higgins’s sentence was greater than necessary, and the district court failed to consider mitigating factors; and (3) the district court improperly enhanced Higgins’s sentence based on prior convictions. For the reasons discussed below, we AFFIRM Higgins’s conviction and sentence.

JULIA SMITH GIBBONS, Circuit Judge. Defendant Jack Groenendal appeals his forty-two month sentence for one count of possession of child pornography. The United States District Court for the Western District of Michigan calculated Groenendal’s base offense level pursuant to a cross-reference under the United States Sentencing Guidelines (“Guidelines”) for trafficking. The district court imposed enhancements for the distribution of prohibited materials in exchange for the receipt of a thing of value and the sadistic or masochistic nature of the materials. The district court also declined to reduce his sentence on account of his “minimal” or “minor” participation. Groenendal claims that the district court erred in calculating his sentence pursuant to the cross-reference to trafficking, applying these enhancements, and denying him a reduction for his minimal role.

For the reasons set forth below, we vacate Groenendal’s sentence and remand for resentencing.

SUTTON, Circuit Judge. The Clean Air Act requires the Environmental Protection Agency to object to an air-pollution permit if any person “demonstrates” to the EPA “that the permit is not in compliance” with the Act’s requirements. 42 U.S.C. § 7661d(b)(2). In August 2006, the Sierra Club petitioned the EPA Administrator to object to a permit issued by the Kentucky Division of Air Quality to the East Kentucky Power Cooperative, claiming it had “demonstrate[d]” non-compliance because the EPA previously had issued a notice of violation to the same company (about the same plant) in January 2003 and had filed a federal-court complaint against the same company (about the same plant) in January 2004. The EPA declined to object. Because it reasonably interpreted § 7661d(b)(2) to mean that the agency may alter its position about a power plant’s compliance with the Act based on intervening events and because the Sierra Club does not challenge the impact of these intervening events on the power plant’s compliance with the Act, we deny the petition for review.

FRIEDMAN, Circuit Judge. The ultimate question in this case is whether the Social Security Act covers physicians participating as medical residents in a graduate training program conducted by a hospital group jointly with a university. The issue arises in a suit by the United States against the hospital group to collect social security taxes under the Federal Insurance Contributions Act (“FICA”) on the stipends the hospital group pays to the residents. The district court granted summary judgment for the United States, ruling (1) that the stipends were wages and not scholarships or fellowships, and therefore not exempt from income tax, and (2) that the residents did not qualify for the exemption from social security tax for “students.” We affirm in part, vacate in part and remand the case to the district court for further proceedings.